The primary purpose of this study is to determine the effects of a full dose (300 mg at hs) of oral micronized progesterone (OMP) on vasomotor symptoms [VMS] (hot flushes/night sweats), on forearm blood flow and on lipid levels and blood pressure in menopausal women without cardiovascular disease and with moderate to severe VMS.

The hypotheses are that progesterone will improve hot flushes, increase endothelium-dependent forearm blood flow and will decrease blood pressure without change in lipid levels.

In this 4-month study, menopausal women are randomized to either placebo or oral micronized progesterone (Prometrium®). Participants maintain a daily diary to keep track of their vasomotor symptoms and other factors. Forearm blood flow will be assessed by venous occlusion plethysmography at baseline and after three months of therapy. Screening tests at baseline to rule out heart disease include measurement of blood pressure and heart rate, electrocardiogram (ECG) and blood tests - fasting blood glucose and lipid profile.

Collection of serum and plasma samples at baseline and end of therapy for analysis of cardiovascular markers (e.g., c-reactive protein) and clotting and fibrinolytic markers. Continued daily diary collection for one month after therapy discontinuation to look for possible rebound effects. Analysis of outcomes will be by analysis of covariates, with final value as the outcome, therapy as factor and baseline values as covariate.

Inclusion Criteria:

1. Menopausal women (final menstrual period one or more but less than 10 years before)
2. No evidence of vascular disease (normal BP; without diabetes mellitus; normal cholesterol levels and non-smoker for at least a year; and normal ECG.)
3. Moderate to severe VMS during the day and night.

Exclusion Criteria:

1. Any menstruation in the preceding year.
2. History of hysterectomy without ovariectomy unless 60 years of age.
3. Use of ovarian hormone therapy (estrogen, progestin, progesterone or androgen) or selective estrogen receptor modulator (SERM) therapy (raloxifene or tamoxifen) in the preceding six months.
4. Body mass index (BMI) over 35 or less than 20.
5. Mean of several pre-treatment blood pressures over 145/95.
6. Documented abnormal cholesterol; abnormal fasting capillary glucose; abnormal angiogram; ECG or exercise stress tests or a diagnosis of diabetes mellitus; or any history suggestive of angina.